Method of recovering storage volume in an underground cavern

ABSTRACT

Storage volume lost in an underground storage cavern as a result of debris collecting at the bottom thereof is recovered by lowering a casing string to a position adjacent the top of the debris, drilling into the debris through the casing string, advancing the casing string into the drilled hole, and thereafter recovering material from the cavern.

United States. Patent References Cited UNITED STATES PATENTS 5/1956Gilmore [72] Inventor Hurshel V. Hendrix Bartlesville, Okla. 839,468

21 Appl. No. 221 Filed [45] July 7, 1969 Patented Sept. 7, 1971 5/1963Primary Examiner-Emest R. Purser AtmmeyYoung and Quigg [73] Assign-teePhillips Petroleum Company [54 METHOD OF RECOVERING STORAGE VOLUME IN ANUNDERGROUND CAVERN 6 Claims, 1 Drawing Fig.

ABSTRACT: Storage volume lost in an underground storage PATENTEB SEP71971 3j603095 INVENTOR.

H. V. HENDRIX A 7' TORNE'VS METHOD OF RECOVERING STORAGE VOLUME IN ANUNDERGROUND CAVERN BACKGROUND OF THE INVENTION It is now common practiceto provide underground storage caverns for hydrocarbons, ammonia andother fluids. Typically, these caverns are formed in a solubleformation, such as a salt bed. In dissolving or otherwise forming acavern, a certain amount of insoluble debris accumulates at the bottom,for example, from pieces of shale or anhydrite which may be present inthe soluble formation. After formation of the cavern, additional debrisoftentimes falls from the top and sometimes damages or severs the tubingutilized for introduction of the stored material into the cavern andremoval therefrom. Since the tubing could not be lowered below the topof the debris, there was loss of storage space represented by the voidswithin the layer of debris. Also, it has not been possible to recoverthe material accumulating within these voids, whether it be stored fluidor displacement liquid.

BRIEF STATEMENT OF THE INVENTION In accordance with my invention, acasing string is lowered to a position adjacent the top of the layer ofdebris. A drill bit is inserted through the casing string and a hole isdrilled into the debris. Thereupon, the casing string is advanced intothe drilled hole. This enables recovery of the storage space representedby the voids in the layer of debris.

DETAILED DESCRIPTION OF THE INVENTION The invention will become furtherapparent from the following detailed description taken in conjunctionwith the accompanying drawing, in which:

The FIGURE is a schematic diagram in vertical section illustrating theapplication of the invention to an underground storage cavern.

Referring now to the FIGURE, I have shown an underground storage cavernl fonned in a soluble formation 11, such as salt. The cavern describedherein is utilized for the storage of hydrocarbons, such as propane,although the invention is applicable broadly to underground storagecaverns provided for the storage of other fluids'such as ammonia orbutane.

Communication between the surface and the cavern is effected by adrilled hole 12 within which is disposed a string 13 of casing supportedwithin the hole by a body 14.0f cement filling the annulus between thehole and casing.

A layer 15 of insoluble debris is shown at the bottom of the cavern 10.This debris consists of impurities such as large pieces of shale,anhydrite or other minerals. Ordinarily, part of the debris accumulatesduring the original formation of the cavern while the rest of it fallsfrom the roof during subsequent use of the cavern.

Material to be stored is introduced into or removed from the cavern by astring of tubing, not shown. For example, in a propane storage cavern,brine may be pumped into the tubing to displace stored material from thecavern whence it passes through the annulus to the surface. Whenadditional propane is to be stored, it is pumped through the annulus,thus displacing brine through the tubing.

It will be evident that the tubing could not heretofore be insertedbelow the top of the layer 15 of debris. Also, in some cases, debrisfalling from the roof has damaged or severed the tubing after the cavernwas placed in operation. It is further evident that the area occupied bythe debris is lost for storage purposes, and that stored or displacementmaterial accumulating within the voids in the layer of debris could notbe recovered due to the difficulty of displacing it from the voidspaces.

In accordance with the invention, I recover the storage volumerepresented by the voids in the debris and permit this volume to beutilized for storage purposes. To this end, I lower a casing string 16through the casing 13 to a region adjacent the top of the layer 15 ofdebris. Thereupon, a drill stem and bit 17 is inserted through thecasing string and a hole is drilled into the layer of debris, preferablyby reciprocation of a cable 18. Preferably but not necessarily, the holeis drilled with cable tools because such holes ordinarily are of largerdiameter than the diameter of the casing string. Thereupon, the casingstring is lowered into the drilled hole, the drill bit is removed, andstored material is recovered from the cavern. This permits the voids inthe layer 15 of debris to be utilized for storage purposes.

As stated, cable tools ordinarily drill a larger hole than that formedby the drill bit so that the casing can be introduced thereinto withoutany difficulty. However, it is within the scope of the invention toutilize rotary tools, in which case it may be necessary to ream theportion of the hole below the casing string 16.

Depending upon the depth of the debris layer, it is oftentimes desirableto repeat the steps of drilling and advancing the casing string. Thus, ahole is drilled a few feet into the debris layer, the casing string isadvanced into the hole, and a further length of hole is drilled. Thesesteps are repeated until the casing penetrates to the desired depthwithin the layer of debris. Most advantageously, of course, the hole isdrilled and the casing advanced to a region adjacent the bottom of thecavern, thereby enabling maximum utilization of the storage volume.

It is a feature of the invention that .the lower end of the easingstring may be slotted or perforated, as indicated at 21. In thisfashion, when total depth has been reached, the casing can be flushedand backflushed to remove silt and fine sand from the region adjacentthe slotted or perforated end of the pipe. This provides access to thevoids in the layer 15 of debris, allowing displacement fluid therein tobe replaced by hydrocarbons.

It will be apparent that I have achieved the objects of my invention inproviding a method of recovering storage volume in an underground cavernwhich has heretofore been lost as a result of debris collecting at thebottom of the cavern. The cost of recovering storage space by thismethod is only a fraction of the cost of providing new storage, as bydissolving additional caverns in soluble formations. Also, the storagevolume can be recovered by my method in only a fraction of the timerequired to construct additional storage facilities.

Other variations and modifications of this invention will be apparent tothose skilled in the art without departing from the spirit and scope ofthe invention.

I CLAIM:

1. In a method of recovering storage volume in an under ground cavernwhich has been lost as a result of debris collecting at the bottom ofthe cavern, the steps of lowering a casing string to a position adjacentthe top of the debris, inserting a drill bit through the casing stringand drilling a hole into the debris, advancing the casing string intothe drilled hole, removing the drill bit to permit the recovery'of fluidfrom the voids in said debris.

2. In the method of claim 1, repetitively drilling increments of holeinto the debris and advancing the casing string into the drilled hole.

3. In the method of claim 2, providing perforations at the lower end ofthe casing string, and flushing fine material from the volumesurrounding the lower section after it has been advanced the desiredamount into the debris.

4. The method of claim 3 wherein the drilling is effected with cabletools and the hole extends to within a short distance of the bottom ofthe cavern.

5. The method of claim 4 wherein the cavern is formed in a saltformation, said cavern contains a light hydrocarbon material storedtherein and including the step of recovery of said light hydrocarbonthrough the casing string.

6. The method of claim 5 wherein the light hydrocarbon is propane.

1. In a method of recovering storage volume in an under ground cavernwhich has been lost as a result of debris collecting at the bottom ofthe cavern, the steps of lowering a casing string to a position adjacentthe top of the debris, inserting a drill bit through the casing stringand drilling a hole into the debris, advancing the casing string intothe drilled hole, removing the drill bit to permit the recovery of fluidfrom the voids in said debris.
 2. In the method of claim 1, repetitivelydrilling increments of hole into the debris and advancing the casingstring into the drilled hole.
 3. In the method of claim 2, providingperforations at the lower end of the casing string, and flushing finematerial from the volume surrounding the lower section after it has beenadvanced the desired amount into the debris.
 4. The method of claim 3wherein the drilling is effected with cable tools and the hole extendsto within a short distance of the bottom of the cavern.
 5. The method ofclaim 4 wherein the cavern is formed in a salt formation, said caverncontains a light hydrocarbon material stored therein and including thestep of recovery of said light hydrocarbon through the casing string. 6.The method of claim 5 wherein the light hydrocarbon is propane.